The present invention relates to a porous clay intercalation compound which is suitable for use in catalysts, absorption separating agents, deodorizers and the like and to a method for its production. In particular, it relates to a porous clay intercalation compound in which hydrogen ions are carried in the pore portions and on the surface portion so as to enhance the solid acidity, and exhibiting a shape selectivity function.
Conventionally, as inorganic porous compounds containing uniform micropores, zeolites and a porous clay intercalation compound are known. The porous clay intercalation compound has slit-shaped pores therein. The layers of a laminar clay mineral, such as, montmorillonite and the like, are cross-linked with inorganic oxide fine particles, such as, Al.sub.2 O.sub.3, ZrO.sub.2 and the like. The inorganic oxide fine particle is called the pillar because it supports the space between the clay layers. The pore diameter of the porous clay intercalation compound can be represented by the distance between layers and the distance between pillars, and it is controlled by the types and sizes of the clay and the pillar to be used, which can be several angstroms to several tens of angstroms. For example, when pillars having a large size are inserted, the distance between layers is widened, while when a clay having a small negative layer charge or a polynuclear cation of high valence is used, the distance between pillars is widened. The pore diameter of the porous clay intercalation compound is uniform, being about a molecular diameter, so that it has a shape selecting function and can be used as a molecular sieve similar to zeolite.
In addition, the porous clay intercalation compound is generally a solid acid and exhibits catalytic activity, making it suitable for use as a shape-selective catalyst. For example, its effectiveness as a cracking catalyst in the petroleum chemistry is described in a plurality of references (E. Kikuchi, T. Matsuda; Catal. Today, 2,297 (1988), M. L. Occeli, R. J. Rennard; Catal. Today, 2, 309 (1988), H. Ming-Yuan, L. Zhonghui, M. Enze; Catal. Today, 2, 321 (1988), M. L. Occeli; Catal. Today, 2, 339 (1988)).
The solid acidity of the prior art porous clay intercalation compound is also determined by the type of clay and the inorganic pillar. For example, in conventional clay, the acidity is relatively strong in montmorillonite; however, it is weak in sodium fluoride tetrasilicic mica which is a species of artificial mica. In addition, in conventional pillars, SiO.sub.2 or TiO.sub.2 shows strong acidity; whereas Cr.sub.2 O.sub.3 inversely shows alkalinity. Due to these facts, the combinations of clay and pillar which enhance solid acidity are limited, and it has been difficult to synthesize a porous clay intercalation compound having both the desired pore diameter and solid acidity.
On the other hand, as porous solid acid catalysts, H-type zeolite and silica alumina are known. However, the pore diameter of zeolite is not more than 10 angstroms, and the size of the molecule which can enter into the inside of the pore is limited to, at most, to molecules no larger than benzene compounds. Treatment of large molecules, such as, polycyclic aromatic compounds, is impossible. In addition, although the silica alumina has a large pore diameter, it is inferior in uniformity, and thus has no shape selectivity.